In a typical Multiplexing/Demultiplexing system, the system bandwidth (or the number of parallel bits) is usually distributed equally to all peripheral cards in the system. This arrangement works fine as long as all the peripheral cards in the system require the same amount of bandwidth. Thus, the Multiplexing/Demultiplexing system of the prior art is configured for known card-types that must conform to the limitations of the Multiplexing/Demultiplexing system.
FIG. 1 illustrates a prior art system for bandwidth allocation which often leads to wasted bandwidth, especially if the peripheral cards, or personality modules, in the system do not require the same amount of bandwidth. The prior art system of FIG. 1 is comprised of multiple slots 4, 6 and 8, for containing peripheral cards, or personality modules, connected to a multiplexer 2 by transmission channels 10, 12 and 14. The system's bandwidth is divided equally amongst all the personality modules regardless of the bandwidth required, thus wasting bandwidth if all modules are not the same. Although three slots are shown, prior art systems can contain a maximum of N slots where N depends on the system's capability.
In the prior art system, bandwidth is wasted if two different types of personality modules, each of which require different amounts of parallel bits, are used. As an example, the first type of module (PIM-A) requires 5 parallel bits for bandwidth and the second type of module (PIM-B) requires 10 parallel bits for bandwidth. A multiplexer which supports 40 parallel bits is utilized to combine the multiple signals from the personality modules for transmission over a single transmission channel. Using only PIM-A modules or using a combination of the two personality modules (PIM-A and PIM-B) in the slots will result in wasted bandwidth because the system distributes the bandwidth equally to all slots.
The 40 parallel bits that the system can support must be divided up equally among the slots. If only PIM-B personality modules are utilized in the system, a maximum of four modules can be used because each module requires 10 parallel bits of bandwidth, since the four modules each requiring 10 parallel bits reaches the maximum number of bits that the multiplexer can support (4 modules×10 bits each=40 bits). However, if only PIM-A modules are utilized in the system, half of the system bandwidth will be wasted. The system can support up to four personality modules. Each of the four PIM-A modules require 5 parallel bits of bandwidth. (4 modules×5 bits each=20 bits) Since the four PIM-A modules only utilize 20 bits of the 40 bits of bandwidth, the remaining 20 bits will go unused and thus be wasted.
Furthermore, typical digital fiber optic systems use time division multiplexing structures with a fixed rate for each channel. For example, a 2.48 Gb/s transmission system might have a capacity of 16 channels, with each channel having a fixed 155 Mb/s bit rate (155 Mb/s×16=2.48 Gb/s). If a signal interface requiring less than 155 Mb/s is inserted into a channel, the excess capacity cannot be accessed or utilized. As an example, some systems provide a dual DS-3 (45 Mb/s) module. This module requires approximately 90 Mb/s bandwidth, but the entire 155 Mb/s channel bandwidth is used. Similarly, some systems use two 155 Mb/s channels to transport a 270 Mb/s SMPTE (Society of Motion Picture and Television Engineers) 259 signal (a type of digital video format), but 310 Mb/s of bandwidth are used.
Thus, there remains a need for a Multiplexing/Demultiplexing system that supports peripheral cards requiring varying bandwidths. A system that allows each card or module to be able to reside in any card slot, and any combination of these personality modules in the system based upon the application is desired.